Nuclear weapons scientists firing exotic, high-speed bullets at plutonium are getting closer to answering a question of academic interest and great political implications: Will aging H-bombs still detonate after decades on the shelf?

The answer could save at least $2 billion on a new bomb-component factory and figure prominently in presidential decisions on restarting nuclear testing and adding new weapons to the U.S. arsenal.

Scientists performed the shots over the last three weeks in the desert outside Las Vegas, and what they discovered remains classified. But they say they gathered the most accurate and detailed measurements ever made of what happens to weapons-grade plutonium under gentle compression and punishing shocks.

Shooting bullets at more than 10 times the speed of a sniper rifle into a hunk of dull gray plutonium make it splatter into molten tar and dust.

But in the split second before the metal goes to smithereens, sundering walls of shock bounce around inside and the metal gets as hot as the surface of the sun.

Scientists at Lawrence Livermore National Laboratory expect the data they gather in those moments will be important for years, perhaps decades, as a foundation for computer predictions of age effects on weapons and nuclear detonations.

Most of those predictions today are based on scientists’ best estimates about the behavior of plutonium under extreme shock conditions like those in an actual bomb. Theoretical approximations served well enough when weaponeers always could perform the ultimate test of a weapon — a nuclear explosion underground at the Nevada Test Site.

But with the end of U.S. nuclear bomb manufacturing in the 1980s and a moratorium on nuclear testing since 1992, scientists need more than theory; they need reliable, accurate data on plutonium both freshly purified and decades old.

“This is like looking in the back of the book for the answer,” said physicist Neil Holmes, lead scientist on the experiments and the gun, which is known as Jasper. “Once you know the answer you can’t guess anymore.”

H-bombs and warheads have thousands of parts, bits of exotic metals and plastics. But the most sensitive component is a hollow, thin-walled ovoid of plutonium packed in high explosive, a miniature atom bomb that serves as the match to ignite thermonuclear fusion.

Being mildly radioactive, plutonium starts disintegrating the moment it is created and within a few years virtually all of its atoms have reshuffled to make room for americium, uranium and helium atoms. In time, it can develop tiny cracks and something like rust.

Even so, scientists’ best current estimates for the viability of weapons plutonium is at least 45-60 years from manufacture. Some think it lasts longer, perhaps 75, 100 years or more.

The Clinton and Bush administrations decided to hedge their bets. Federal weapons officials are storing thousands of old plutonium cores from dismantled weapons and are planning a new plutonium core factory to replace Rocky Flats, a weapons plant outside Golden, Colo., that closed in 1989 after plutonium fires and other environmental problems.

The new plant, called the Modern Pit Facility, would make 125 to 450 plutonium cores a year starting as early as 2018 and cost $2 billion to $4 billion, depending on its size and date of construction.

If plutonium ages gracefully and still responds to explosive compression the same at age 70 as at infancy, the new bomb plant could be smaller and less expensive, or it could be delayed for years.

If plutonium becomes brittle or flaky at a younger age, federal weapons authorities will urge a larger Modern Pit Facility, and the president is likely to be faced with requests for new weapons designs and a resumption of nuclear testing.

That’s how much could be riding on the gun shots in Nevada and other experiments on plutonium.

“It’s really the first aging shot that’s been done,” said Bruce Goodwin, Livermore’s chief of weapons research and a plutonium expert. “It doesn’t answer the final question, but it begins to answer the question.”

Getting those answers can take extraordinary engineering. No other scientific team had managed to get gentle compressions of plutonium on a gun. Livermore engineers came up with a designer bullet of more than 100 layers of different metals and plastic.

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